A number of different video encoding standards have been established for encoding digital video sequences. The Moving Picture Experts Group (MPEG), for example, has developed a number of standards including MPEG-1, MPEG-2 and MPEG-4. Other examples include the International Telecommunication Union (ITU) H.263 standard, and the emerging ITU H.264 standard. These video encoding standards generally support improved transmission efficiency of video sequences by encoding data in a compressed manner.
Video telephony (VT) permits users to share video and audio information to support applications such as videoconferencing. Exemplary video telephony standards include those defined by the Session Initiation Protocol (SIP), the ITU H.323 standard, and the ITU H.324 standard. In a VT system, users may send and receive video information, only receive video information, or only send video information. A recipient generally views received video information in the form in which it is transmitted from a sender.
Preferential encoding of a selected portion of the video information has been proposed. For example, a sender may specify a region-of-interest (ROI) to be encoded with higher quality for transmission to a recipient. The sender may wish to emphasize the ROI to a remote recipient. A typical example of an ROI is a human face, although a sender may wish to focus attention on other objects within a video scene. With preferential encoding of the ROI, a recipient is able to view the ROI more clearly than non-ROI regions.
An ROI may be preferentially encoded by allocating a greater proportion of encoding bits to the ROI than to non-ROI, or “background,” areas of a video scene. Skipping of a non-ROI area of a video frame permits conservation of encoding bits for allocation to the ROI. The encoded non-ROI for a preceding frame can be substituted for the skipped non-ROI in a current frame. Alternatively, the skipped non-ROI can be interpolated. In either case, skipping encoding of the non-ROI area of a frame permits enhanced encoding of the ROI.